1. Field of the Invention
This invention pertains generally to the field of satellite communications and antennas for satellite ground terminals, and is more specifically directed to multi-band dish antennas.
2. State of the Prior Art
Ka-band satellite data systems provide a very good option to the consumer seeking broadband Internet connectivity where no terrestrial alternatives such as cable or telephone line based broadband service are available. Satellite Internet access is currently available and has found favorable market acceptance. The ability to add a Ku-band high-powered DBS satellite delivered TV service to the Ka-band Internet access offering at minimal added cost to the consumer is expected to make the Internet access service even more compelling. However, the prospect of having two satellite antennas added to the exterior of their homes may be enough to dissuade many customers. In those areas already serviced by DSL and cable Internet access, a lower price and equal-to-better performance of satellite Internet access may not be enough to overcome that customer""s reluctance to put a relatively large and expensive satellite antenna on the outside of their home. This might be particularly true if that consumer already has a high-powered DBS dish in place for an existing satellite delivered TV service.
This difficulty could be overcome by providing a small, relatively low cost single dish antenna capable of handling the two-way Ka-band data link as well as reception of one or more Ku-band DBS satellites.
Many existing home terminal DBS satellite terminal antennas are capable of receiving DBS service from two satellites. The small dish reflectors of these antennas have narrow beam width and are limited to reception of satellites which are close to each other along the geostationary arc. The signals from two adjacent satellites are reflected to slightly spaced apart focal points at the dish antenna and are received by two side-by-side feed horns, each positioned at or near one of the focal points. Each horn feeds a separate block down-converter low noise amplifier unit to amplify and convert the high frequency satellite transmissions to lower intermediate frequencies which are delivered via coaxial cable to an indoor DBS receiver close to the TV set for channel selection and other signal processing and control functions. Dual feed satellite TV antennas of this type are in widespread use and the components for these are readily available at low cost due to their high volume manufacture and mature design. Integrated feed horn-with block downconverter LNA modules (LNBF modules) for Ku-band DBS TV reception can be purchased in quantity at low cost.
Ka-band Internet access service requires two-way communication between the ground terminal at the subscriber""s location and a data communications satellite in geostationary orbit. Computer keyboard or mouse input from the subscriber is transmitted from the ground terminal antenna to the satellite, which returns the subscriber input to a data center maintained by the access provider and connected to the Internet backbone through appropriate routers and server computers. Data is returned from the Internet to the provider""s data center in response to the subscriber""s input, from where it is transmitted up to the data satellite which in turn transmits the data to the subscriber""s geographical location where the satellite transmission is received by the subscriber""s ground terminal antenna. Standard Ka-band satellite communication frequencies are in a 30 GHz band for the uplink from the subscriber antenna to the data satellite and a 20 GHz band for downlink or satellite to ground signal. The Ka-band uplink and downlink signal requirements can be satisfied by a small transmitter/receiver package mounted on the subscriber""s antenna.
A single dish solution to Ka-band Internet access bundled with Ku-band DBS reception therefore requires a dish antenna capable of receiving at 12 GHz and 20 GHz and of transmitting at 30 GHz frequencies.
Tri-band operation of a single reflector dish antenna is possible using a so-called co-boresighted tri-band feed to illuminate the reflector dish at each of the three frequency bands of interest. However, in addition to being costly, it was found that these kinds of tri-band feeds fail to deliver the performance necessary in a reflector dish antenna small enough to find general acceptance among potential subscribers.
Frequency selective surfaces (FSS) have been used as subreflectors on reflector dish antennas for separating signals between a prime focus and an image focus. Frequencies reflected by the FSS are reflected to the image focus of the subreflector while those frequencies to which the FSS is transparent pass through the FSS to the prime focus of the dish reflector. Such an arrangement is shown, for example, by Matson et al. in U.S. Pat. No. 3,231,892. However, FSS technology has been generally limited to military, space and certain specialized applications such as microwave communications systems, and has not been applied in low cost consumer satellite terminals.
This invention provides a lower cost, higher performance solution to the problem of triband operation of a single dish satellite antenna for providing bundled Ka-band two-way broadband Internet access and Ku-band direct broadcast satellite television service. The novel antenna has a parabolic main reflector dish with an offset prime focal point; a frequency selective surface sub-reflector defining an image focal point; a first feed supported at the prime focal point, a second feed supported at the image focal point; a Ku-band block down-converter low noise amplifier system connected for receiving Ku-band direct broadcast satellite television signals reflected from the dish to one of the first feed and the second feed; a Ka-band transmitter connected to the other one of the one feed and the second feed for illuminating the dish with Ka-band uplink transmissions; and a Ka-band low-noise block-down converter connected for receiving Ka-band downlink signals reflected from the dish to either one of the first feed and said second feed. The dish is mounted on a mast which in turn is fixed to a supporting structure such as a pole or the roof or side wall of a house. The dish mount includes azimuth, elevation and skew adjustments for the dish relative to the mast. Accordingly, two-way Internet access and satellite television service provided by at least two nearly or actually collocated satellites can be delivered to a subscriber by installation of a single ground terminal satellite antenna reflector dish at a subscriber location.
An important advantage of this invention is that it can use a flat or planar frequency selective surface subreflector.
Still another advantage of this invention is that the antenna makes use of readily available, off the shelf, low cost Ku-band DBS components for reception of the DBS TV satellite service.
The satellite antenna includes a feed/transceiver support boom fixed to the dish. The first feed, the second feed, the Ku-band block down-converter low noise amplifier, the Ka-band transmitter and the Ka-band block-down converter low-noise amplifier are all preferably supported on the boom.
Optionally a weather resistant protective enclosure may be provided containing the frequency selective surface and one or both of the first feed and the second feed such that heat generated by operation of the Ka-band transmitter operates to warm the protective enclosure thereby to reduce accumulation of snow and ice thereon.
In one form of the invention the Ka-band transmitter and the Ka band low noise block downconverter are contained in a Ka-band transceiver housing, the housing is supported to the boom, and the second feed and the frequency selective surface are all mounted to the transceiver housing, and including fasteners for detachably supporting the housing to the boom.
In a presently preferred form of the invention the first feed comprises side-by-side Ku-band feed horns and the Ku-band block down-converter low noise amplifier system comprises separate block down-converter low noise amplifier units each operatively associated with one of the Ku-band feed horns such that direct broadcast satellite television signals may be received from two, or more, different satellites spaced along the geostationary arc, and further comprises an adjustment for orientation of the dish in skew relative to the mounting mast.
Another important feature of the novel antenna is that it may be installed in a baseline configuration for delivering broadband Internet access only, and later the antenna may be easily and quickly upgraded in the field to provide DBS satellite TV service at the option of the subscriber. To this end the antenna has a Ku-band subassembly or module removably supported on the boom, the subassembly comprising one or more Ku-band feed horns supported at or near the prime focal point and a Ku-band block down-converter LNA associated with each Ku-band feed horn. The subreflector is interchangeable between a non-selective reflector such as a metal plate subreflector and a frequency selective surface subreflector. The antenna operates in a data only configuration in the absence of the Ku-band module and can be converted from the two way Ka-band data only configuration to the bundled data plus DBS configuration by installation of the Ku-band subassembly on the boom and replacing the metal plate subreflector with a frequency selective surface subreflector.
The Ku band module may have side-by-side Ku-band feed horns and two low noise block down-converter units each operatively associated with one of the Ku-band feed horns, all packaged in a common housing, such that direct broadcast satellite signals may be received from different satellites spaced along the geostationary arc. For purposes of alignment of the side-by-side Ku-band feeds a skew adjustment of the dish relative to said mast may be provided.
The Ka-band transmitter and Ka band receiver can be contained in a Ka-transceiver housing, the Ka-band feed horn also mounted to the transceiver housing, and the transceiver housing detachably supported to the boom.
The invention may also be understood as a method for delivering two-way Internet access and direct broadcast satellite television service to a subscriber by installation of a single satellite antenna reflector dish at a subscriber location. The method includes the steps of providing a Ka-band data satellite and one or more Ku-band direct broadcast satellites, the satellites being nearly or actually collocated along the geostationary arc; providing a satellite antenna at a subscriber location having a single parabolic main reflector dish with an offset prime focal point, two wide-band feed horns, a 20 GHz Ka-band LNBF, a 12 GHz Ku-band LNBF and a 30 GHz Ka-band transmitter, each LNBF and the transmitter having a waveguide connection; connecting one of the feed horns to the waveguide connection of the 20 GHz Ka-band LNBF and the 30 GHz Ka-band transmitter, and the other feed horn to the waveguide connection of the 12 GHz Ku-band LNBF, or alternatively connecting one of the feed horns to the waveguide connection of the 20 GHz Ka-band LNBF and the 12 GHz Ku-band LNBF, and the other feed horn to the waveguide connection of the 30 GHz Ka-band transmitter; providing a flat frequency selective surface subreflector for illuminating the dish with the output of each of the two feed horns; and aligning the dish for simultaneous reception of transmissions from the Ka-band satellite and the Ku-band satellite by the Ka-band LNBF and the Ku-band LNBF respectively and for uplink communication to the Ka-band satellite by the Ka-band transmitter.
The invention also includes a method for upgrading a Ka-band two-way satellite data communications terminal antenna to simultaneously receive Ku-band DBS satellite television reception from a Ku-band direct broadcast satellite nearly or actually collocated along the geostationary arc with a Ka-band data satellite, the antenna having a single parabolic main reflector dish with an off-axis prime focus, a metal plate subreflector defining an image focus, a Ka-band feed horn at the image focus, and a Ka-band transceiver connected to the Ka-band feed horn, the method comprising the steps of replacing the metal plate subreflector with a flat frequency selective surface subreflector and installing one or more Ku-band LNBFs at or near the prime focus of the dish.
In a more general sense the invention is directed to a multi-band antenna comprising a parabolic reflector dish with a prime focus and a frequency selective surface subreflector defining an image focus; a first feed horn at the prime focus and a second feed horn at the image focus; first, second and third radio-frequency communications modules, each of the modules comprising either a radio-frequency transmitter or a radio-frequency receiver, the modules operating on three different frequency bands such that the frequencies of only a first and a second of the frequency bands are related by a factor of approximately two, or less, and a third of the frequency bands is removed from at least one of the first and second frequency bands by a factor greater than two; the two of the modules operating at the first and second of the frequency bands being operatively connected to one of the first and second feed horns and the third of the modules operating at the third frequency band being operatively connected to the other of the first and second feed horns. The frequency selective surface subreflector is preferably a flat surface subreflector and the first and second feed horns are each a wide band feed horn such as a corrugated or scalar aperture wide band feed horn. In a presently preferred form of the multi-band antenna the first of the modules is a 20 GHz band receiver, the second of the modules is a 30 GHz band transmitter and the third of the modules is a 12 GHz band receiver, and the first and second modules are connected to the second feed horn while and the third module is connected to the first feed horn.
These and other features, advantages and improvements of this invention will be better understood by reference to the accompanying detailed description of the preferred embodiment taken in conjunction with the accompanying drawings.